Insecticide susceptibility of Anopheles gambiae s.l and identification of some resistance mechanisms in Kwilu Province in the Democratic Republic of Congo

INTRODUCTION: the control of the mosquito malaria vectors by the National Malaria Control Programme of the Democratic Republic of Congo (DRC) relies mainly on the use of long-lasting insecticide-treated nets (LLINs). However, the widespread emergence of resistance to pyrethroids is jeopardizing this control strategy. The objective of this study is to determine the status and resistance mechanisms involved in Anopheles gambiae s.l. population of DRC. METHODS: pre-imaginal stages of An. gambiae s.l. were collected and standard WHO bioassays were performed on adult An. gambiae s.l. reared in the laboratory from larvae collected from different sites in the study area. The bioassays with the synergist PBO were also performed to determine the likely implication of oxydases in the resistance. The alleles of knock down resistance (Kdr) gene and species of anopheles were determined by PCR-RLFP. RESULTS: all Anopheles mosquitoes tested belonged to the Anopheles gambiae complex. An. Gambiae (69.6%) was predominant, followed by An. Coluzzii (25.6%) and (4.8%) hybrids (An. gambiae/ An. coluzzii). Bioassays showed phenotypic resistance to the main insecticides used in the region, notably pyrethroids (deltamethrin, permethrin) and organochlorine (DDT). Only bendiocarb caused 100% mortality. Metabolic resistance involving oxidase enzymes was also detected using the synergist PBO after exposure to deltamethrin. The L1014F allele frequency of Kdr gene was detected in samples collected from all sites at varying frequencies (0.61-1.0). CONCLUSION: this study brings additional information on malaria vectors resistance to insecticides. It has shown cross-resistance to DDT and pyrethroids as well as the presence of Kdr gene. PBO significantly improved the effectiveness of deltamethrin. The results of this study can be helpful to policy makers in decision making for vector control programmes in the region.